1. Field of the Invention
This is a continuation Ser. No. 760,362, filed June 28, 1985 now abandoned.
The present invention relates generally to the removal of particulates from a flowing air stream, and more particularly to the removal of submicron particles using a rotary spray scrubber.
The collection of submicron particles is problematic. While conventional collection technologies, such as electrostatic precipitators, venturi scrubbers, and baghouses, are capable of relatively high collection efficiencies, the utilization of each of these methods suffers from drawbacks. Electrostatic precipitators require constant adjustment of the operating voltage level for efficient collection of submicron particles. Venturi scrubbers incur very high energy costs in fan pressure drop requirements to achieve an acceptable collection efficiency. Finally, the bag filters in baghouses quickly become plugged with very fine particulates (particularly with oil-based smoke particles which stick to the cloth filters) and must be frequently replaced at a substantial cost.
Conventional water scrubbers rely on the physical impaction of the particulates in an air stream with water droplets to remove the particles from the air stream. The collection efficiency of water scrubbers increases when the amount of liquid is increased or the amount of gas being scrubbed is decreased. Conventional water scrubbers use low pressure pumps (typically 30 psi) with large volumes of water (typically 20 to 40 gal/1000 cfm gas). The scrubbing action is accomplished with large water droplets (1000 to 3000 microns) which move at low speeds (30 to 60 ft/sec). When scrubbing submicron particles, conventional water scrubbers achieve collection efficiencies which are typically lower than 50%, usually between 20% and 30%. While the collection efficiency can be increased by forming much smaller droplets or by further large increases in the amount of water sprayed, these alternatives require either high pressure pumps (3000 to 5000 psi) and/or a large water flowrate. Such additional pumping requirement renders conventional water scrubbers impractical for removing submicron particles because of both high capital costs and high operating costs due to high energy consumption.
For the above reasons, it would be desirable to provide a water scrubbing system for the removal of submicron particulates from a gas stream without excessive requirements for water or energy.
2. Description of the Prior Art
A rotary spray scrubber of the type of the present invention is described in U.S. Pat. No. 4,242,109 to Edwards. The scrubber includes a conduit for directing the particulate-laden gas stream in a first direction. An axial impeller induces flow of the gas through the conduit. A rotary dispersion device attached on a common shaft with the impeller and located immediately downstream thereof directs a spray of droplets into the flowing air stream. The nature of the rotary dispersion device is not discussed in detail in the patent.
Certain machines incorporating the teachings of the subject patent have been manufactured and sold by EMCOTEK Emission Control Technology, Visalia, Calif. 93291. The dispersion device employed in these machines is illustrated in FIG. 1 and comprised a six-inch diameter hub 10 including a pair of spaced-apart disks 12 joined by a perforated sheet metal periphery 14. The perforations 10 comprised about 50% of the peripheral surface area. Water was fed into the hub 10 through an opening 18 in one of the disks and the hub rotated to generate a spray. The hubs were placed in conduits (reference no. 15 in the Edwards patent) having a diameter of 18 inches. Using this device, collection efficiencies of submicron particles above 50% could not be achieved.